My girlfriend wants to be poly again

Before I started dating my girlfriend about 5 years ago we were just friends and she had a boyfriend. At some point we started dated while she was still with her boyfriend (I did not date the boyfriend as I am a lesbian and it just didn’t feel right to be in that kind of poly relationship). Idk if it’s just bc we were friends and I knew her boyfriend wasn’t the best but I never had any jealousy with him, so there were no issues in our relationship.

They did break up some months later for her own reasons.

I’ve known from the begging she was poly and I had some past trauma that’s really made it hard for me to be open to being poly again. She doesn’t want to date another guy she just wants to sleep with them but I’ve found it really hard to find ways to get over being jealous. She has started to resent me for not making even the littlest steps to being more open to the idea. And to be honest I’m upset with myself also bc I know this would make her happy and I want it to make her happy.

I’m really looking for any kind of advice